In the project work we built a reader, which measures the resonant frequency of a passive SAW-resonator. We are able to calculate the temperature because the resonant frequency depends on it.

The goal of this diploma work was to realise the RFID-Reader on 1-2 PCB's. So we are no more bounded to the laboratory. To be independent we mainly had to build the sinus generator for the intermediate frequency and the local oscillator. The analysis should be implemented in a DSP. To minimise internal and external electromagnetic disturbances, the RF-section should be covered with a shield.

The main structure of the RF-section was proved in the project work. We continued it with additional features. For an optimal use of the transmit amplifier and to minimise the noise power of the receiver, we inserted a strait band pass filter in transmit and receive path. We had to cascade two switches for higher isolation between transmit and receive path. The structure of the PCB design was given of the shield, which we got from Elektrobit AG.

We dimensioned and realised the local oscillator in a PLL with a fractional-N synthesizer. Thereto we analysed the loop filter on control aspects and built a discrete VCO. To generate the intermediate frequency exibly, we realised it with a DDS. So we are able to create different frequencies and can switch the source on and off. We built a preamplifier with variable gain that we can control the whole range of the ADC. The DSP controls all of these chips.

We analysed the measured signal with two methods. In the first method the frequency of the signal is calculated with a constant stimulation frequency by the FFT. For a higher accuracy, we calculate DFT values around the peak of the FFT. With overlaying many signals, we can determine the received noise.

We successfully built a first prototype in this diploma work. With it we are able to show, that we can measure wireless the resonant frequency of passive SAW-Resonators over a long distance.